Muscle Physiology – Part 1

Recently, Jacob Schepis, Brian Minor & myself presented a nearly 4 hour-long webinar on some things hypertrophy. I’d love to say all things, but I know that I had to cull massive amounts of information from my slides, and I’m sure the boys were the same. All of us went over time by a good 20 or so minutes… There’s just so much cool stuff to talk about when it comes to growing muscle!

Firstly, thank you so much. It is truly mind-boggling to be able to do these things and speaking on behalf of Brian and Jacob also, we are so appreciative and grateful for all of you who are interested in and support the work that we do. No matter how little it actually feels like “work”. Additional shout out to those international folk who were up at ungodly hours just to join in the fun!

Secondly; again, thank you for sticking with us through a longer than planned presentation, with some minor teething issues. This was the first time we had done something like this. Personally, I think it went relatively well, but there’s always room for improvement. If you do have any thoughts or feedback, please free to contact me at: lyndon@jpshealthandfitness.com.au. It is surprisingly difficult to gauge the consumer experience with these sorts of things, so any ideas or criticism is welcome. Although with that said, many of you have reached out through Instagram and that has been truly flattering. If you’d simply like to see more of this sort of thing, please be sure to let myself or one of the others know!

If you didn’t tune in:

Oh boy (or girl, #teamequality)… What are we going to do with you? Nah, for real, this is what this blog post is for. The replay is still available for purchasing HERE if you’re interested, but if not, I thought I would at least try to summarise my section of it for you.

Muscle Growth Physiology

Whenever I discuss physiology, which is a lot (I don’t advise hanging out with me, I’m not very fun), I like to preface any discussion with what actually physiology refers to.

Now that seems obvious, but you’d be surprised at how few people do this when conveying information and you’d be surprised at how few things that you or anyone can actually clearly define without a little bit of prompting. Quite often we have vague comprehension of something, enough of a understanding to engage in a conversation, but when contentious or complicated issues arise our apprehension begins to wane.

Let’s use physiology as an example. Today, in order to actually gather some data to support my claim, I asked a number of JPS clients: What is physiology?

The answers were as follows:

– “It’s science related…” – “I think it has to do with biology or something like that…” – “That’s the one with the cells and things yeah?”

A number of other responses were given, but you get my point.

Keep in mind however, I would say that JPS clients are above average in their understanding of training and nutrition related topics, but quite simply, they are people and people can’t know everything. It’s not their job to be an expert in this field.

This example of having a rough idea about something, but not quite completely grasping the concept is pervasive. The more I teach, present, coach and mentor, the more I have come to realise the importance of grounding a discussion distinct definitions. This provides a solid foundation and point of mutual agreement that any further information can be built upon, rather than initiating a conversation a point of divergent understandings.

So, with that preamble out of the way, what is physiology?

Physiology relates to function, primarily, but not exclusively on the cellular/tissue level. It is inherently related to anatomy, which is the study of structure. Structure and function are fundamentally inseparable concepts and you cannot influence one without impacting the other. Both of these fall under the broader branch of biology, which is the study everything that is alive.

Remember that when you see the word physiology thrown around in mainstream fitness. As “science” has become more of a selling point in recent years, words such as “physiology” are becoming more prevalent, although you can often see that they are not understood completely as they often used incorrectly and out of context more times that not.

The final point I will make on the point on broader physiology is this:

For every gimme, there’s a gotcha.

Meaning; there’s no such thing as “hacking your body”. There’s stimuli, adaptations, improvements in some regards and trade-offs in others. Now that’s not to say that net-positives cannot be acquired over time with an intelligent approach, but as Andy Galpin likes to say, “there’s no free passes in physiology”.

Now that we have established what physiology is, up next: muscle growth. Again, it may seem semantic or superfluous, but it is important to know what is occurring when muscle tissue actually grows. Growth is not a macroscopic (visible to the naked eye) process, it’s not just curls = bigger biceps. Overtime, muscle growth reveals itself on the macroscopic level, but it is the result of almost infinite microscopic processes prior to that.

Muscle growth is the result of two potential physiological procedures: hypertrophy and hyperplasia.

Hypertrophy is the increase in size of an organ or tissue, via an increase in cell size. Conversely, hyperplasia is the increase in size of an organ or tissue, via an increase in cell number.

To address the latter first, evidence of hyperplasia occurring in humans is equivocal. It has been demonstrated more convincingly using animal models, however many of the interventions are impractical for human use. This is not to say that it conclusively does not occur in humans however. What the evidence does indicate though, is that if it does, it is to a very small degree.

Hypertrophy though is a different story; there is nothing contentious about its existence. What mechanisms cause it, what signalling pathway does what, or how to maximise it from a training perspective? Sure, plenty of issues still need investigating there. But fundamentally, the fact that hypertrophy occurs is indisputable.

So it seems pretty clear that increasing muscle size, via hypertrophy, the increase in individual cell size is the basket we want to be putting our eggs in. Therefore, any discussion from this point onwards will use hypertrophy and muscle growth synonymously, unless stated otherwise.

The next logical question would then be; how do cells increase in size?

Cells change in size due to an imbalance between protein synthesis and protein breakdown. When the cell is constructing more protein than it is deconstructing, the cell increases in size. This is called anabolism and results in the storage of energy.

When the cell is metabolising more of its own protein than it is building (breakdown exceeds synthesis), the cell reduces in size. This is called catabolism and results in the release of energy.

Furthermore, synthesis and breakdown are interrelated processes. As stated earlier, physiology doesn’t do free lunches. You cannot completely maximise one and minimise the other, nor should you want to. …

A few examples of the connectedness of synthesis and breakdown are:

Eating protein – Contrary to popular belief, eating protein doesn’t increase synthesis and reduce breakdown. Protein synthesis and breakdown both increase when protein is consumed. Though doing so typically results in a net-balance that favours synthesis, but it is not an inverse relationship as it is often described.

Gene knockdown studies – Mice that are engineered to so that they have diminished ability to breakdown muscle proteins end up smaller and weaker than regular mice. Breakdown is important in maintaining health, function and adaptability.

Damaging workouts – Exercise induced muscle damage increases both muscle protein synthesis and breakdown. Is this beneficial for growth? You’ll have to wait until part 2.

…

Ok, so far we have established that muscle growth is predominantly achieved by an increase in the size of existing cells, and the way those individuals cells increase in size, is by building more proteins than they breakdown. Predictably, we must now cover what we can do in order to get our cells to skew protein balance towards net-synthesis.

Although there are many factors that can influence this balance (which will be covered later), the most powerful (at least in drug-free realms) is inarguably resistance training. The ability of resistance training to impact protein-balance with such great magnitude is fundamentally why resistance training is the best thing you can do to improve your long-term body-composition. No dietary, supplemental or other exercise strategy will improve how you look, more so than scientifically sound and structured weight lifting.

Before we go any further though, if we are going to discuss resistance training and maximising its hypertrophic efficacy, then some fundamental concepts of sport science and exercise physiology must be covered first. The best outcomes aren’t generated from getting caught up on the latest research; you achieve results though the basics.

So let’s build a framework for understanding how muscles, and specifically their fibres function before we go any further. We will then be in a better position to create or critique a specific muscle-building methodology.

The 4 key concepts of muscle function as they relate to us here are:

Sliding Filament Theory: The explanation of muscle contraction that is a result of muscle proteins sliding past one another in order to create movement and shorter whole muscle length, while the muscular proteins all remain constant in length. Myosin filaments (thick) reach out and grab onto the Actin filaments (thin), termed cross bridging, and then pull them towards the midline of the sarcomere (the basic unit of skeletal muscle).

The Size Principle: Motor units innervate muscle fibres and as demands of the task increase; incrementally larger motor units (and fibres) are recruited. Under normal conditions (non-fatigued), low force requirements will only recruit low-threshold motor units, which govern small (oxidative) and few (<100) fibres. High force demands (or fatigue) will recruit large motor units, which innervate the largest and the most fibres (>1500), ON TOP of all the other lower threshold motor units.

The Force-Velocity Relationship: Muscle fibres can produce more force when they are able to contract slowly, than when they are forced to contract more quickly. This is due to slower contraction rates allowing for greater amounts of simultaneous cross bridging between actin and myosin filaments. More hands make light work.

The Length-Tension Relationship: Muscle fibres produce differing amounts of force at differing muscle lengths. The length-tension relationship is the combination of two concepts, the Active & the Passive length-tension relationship. The ALTR produces peak tension when the muscle is at the optimal length for maximal A&M cross bridging. The PLTR produces peak tension when the muscle is lengthened to very long lengths due to the elastic properties of muscle cells.

That brings us to the end of the first instalment in the series. Today we covered muscle physiology basics and looked at what muscle growth actually is on the cellular level. Next time we will move into the more applied aspects of physiology, examining the ways in which protein balance is altered by training induced mechanisms.

author: Lyndon Purcell

Lyndon is the Head Science Consultant of the JPS Health & Fitness team. Having completed his Bachelor of Exercise Science, Lyndon is a
huge proponent of using science and evidence based methods to guide training and nutrition. Body composition (fat-loss and muscle growth) is his area of expertise.

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